The present invention pertains to the field of distillation of fluid mixtures, and in particular to processes for the production of electronic-grade oxygen or other ultra-high purity fluids from a standard-grade supply.
Liquefied atmospheric gases are increasingly used in the electronics industry. Frequently, however, the time required to build a new, full-scale, gas plant is too long or the initial gas requirements of an electronics facility are much less than the ultimate capacity of such a gas plant. In these instances, there is a need for a small system which can convert locally available standard-grade liquid into electronic-grade liquid. Typically, standard-grade liquids contain quantities of light impurities and heavy impurities which are considered undesirable for electronics applications.
There are several prior art processes for the production of electronic-grade oxygen, often called ultra-high purity oxygen. Several processes are directed to producing the oxygen (and sometimes also nitrogen) by cryogenic distillation of air, not by purification of standard-grade oxygen. Examples include: U.S. Pat. Nos. 4,560,397; 4,615,716; 4,977,746; 5,049,173; and 5,195,324. Production of electronic-grade oxygen by direct separation from air can be efficient but requires a relatively long procurement and construction schedule.
Some processes aimed at the direct production of electronic-grade oxygen from standard-grade liquid oxygen also have been disclosed in the prior art. Examples include: U.S. Pat. Nos. 4,780,118; 4,867,772; 4,869,741 and 5,682,763.
U.S. Pat. No. 4,780,118 discloses a process which uses two columns configured in a direct sequence. The feedstock enters the first column, which rejects the light impurities, from the top. The bottom stream from the first column, which is light-lean and contains oxygen and heavy impurities, is passed to the second column, from which the desired oxygen product is recovered from the top. The first column is fitted with a reboiler, and the second column is fitted with a condenser.
U.S. Pat. No. 4,867,772 discloses a process which uses two columns configured in an indirect sequence. The feedstock enters the first column, which rejects the heavy impurities, from the bottom. The top stream from the first column, which is heavy-lean and contains oxygen and light impurities, is passed to the second column, from which the desired oxygen product is recovered from the bottom. The first column is fitted with a condenser, and the second column has both a reboiler and a condenser.
U.S. Pat. No. 4,869,741 discloses a process which uses two columns configured as a main column and a side stripper. Both columns operate at the same pressure. Use of a side stripper eliminates one condenser.
For energy efficiency, U.S. Pat. Nos. 4,780,118; 4,867,772; and 4,869,741 utilize a closed loop heat pump to operate the reboilers and condensers.
U.S. Pat. No. 5,682,763 discloses a number of distillation configurations, some of which have been described previously. The improvement disclosed by U.S. Pat. No. 5,682,763 is the use of an external process stream to drive the reboiler and condenser--thereby eliminating the compression equipment associated with the previous disclosures.
It is desired to have a more economical means of removing light impurities and heavy impurities from standard-grade supply.
It is further desired to have improved processes for the purification of oxygen to produce electronic-grade oxygen.
It is still further desired to have improved processes for the purification of other fluids.
It also is desired to have improved processes for the production of electronic-grade oxygen or other ultra-high purity fluids which processes overcome the difficulties and disadvantages of the prior art processes to provide better and more advantageous results.